As wireless communications technology continues to evolve, there is a focus on improving both reliability and speed. In recent years, technologies such as multiple-input-multiple-output (MIMO) and carrier aggregation have been used to increase both speed and reliability of a wireless connection. At a high level, MIMO and carrier aggregation allow multiple radio frequency (RF) signals to be simultaneously transmitted and/or received by a device. These RF signals are generally transmitted at different frequencies and then separated by a receiving device to obtain the data therein. While this process is relatively straightforward when the frequencies of the RF signals are far apart, it becomes significantly more complex when they are not. This is due to the RF front end circuitry that is responsible for separating the received RF signals. Conventional RF front end circuitry often utilizes a tiered filtering approach in which RF signals are first separated into relatively large RF frequency bands, and then filtered with increasing granularity as they move downstream from an antenna, ultimately being separated into one or more RF operating bands. For example, a first filter in conventional RF front end circuitry may separate low-band RF signals (i.e., RF signals with a frequency between 700 MHz to 1000 MHz) from mid/high-band RF signals (i.e., RF signals with a frequency between 1800 MHz and 2700 MHz), a second filter downstream from the first filter may separate mid-band RF signals (i.e., RF signals with a frequency between 1800 MHz and 2200 MHz) from high-band RF signals (i.e., RF signals with a frequency between 2300 MHz and 2700 MHz), and a number of band filters downstream from the second filter may separate the mid-band RF signals and the high-band RF signals into separate RF operating bands (e.g., 3rd Generation Partnership (3GPP) Long Term Evolution (LTE) operating bands).
Due to the relatively large separation between low-band RF signals and mid/high-band RF signals (i.e., ˜800 MHz), the first filter in such a system is generally capable of separating these signals without issue. However, the narrow separation between mid-band RF signals and high-band RF signals (i.e., ˜100 MHz) makes such a task much more difficult. Designing a filter with the required bandwidth to pass both mid-band RF signals and high-band RF signals may reduce the achievable selectivity of the filter. Due to this limited selectivity, mid-band RF signals at the upper end of the frequency band and high-band RF signals at the lower end of the frequency band will be cross-contaminated, and may reduce the performance of the RF front end circuitry such that certain combinations of operating bands are not usable for carrier aggregation and/or MIMO.
To address these issues, RF front end circuitry 10 has been proposed as shown in FIG. 1. The RF front end circuitry 10 includes a primary antenna 12, a secondary antenna 14, primary antenna swapping circuitry 16, secondary antenna swapping circuitry 18, a front end diplexer 20, reconfigurable RF filtering circuitry 22, first band filtering circuitry 24, and second band filtering circuitry 26. The primary antenna swapping circuitry 16 is coupled between the front end diplexer 20 and the primary antenna 12. The secondary antenna swapping circuitry 18 is coupled between a secondary RF signal node 28 and the secondary antenna 14. The reconfigurable RF filtering circuitry 22 is coupled between the first band filtering circuitry 24, the second band filtering circuitry 26, and the front end diplexer 20.
The primary antenna swapping circuitry 16 includes a number of primary antenna swapping switches SWPAS. The secondary antenna swapping circuitry 18 includes a number of secondary antenna swapping switches SWPAS. Together, the primary antenna swapping switches SWPAS and the secondary antenna swapping switches SWPAS are configured to couple one of the primary antenna 12 and the secondary antenna 14 to the front end diplexer 20 and couple the other one of the primary antenna 12 and the secondary antenna 14 to the secondary RF signal node 28. While not shown in order to avoid obscuring the drawings, the secondary RF signal node 28 is generally coupled to secondary RF filtering circuitry in order to separate secondary RF receive signals into their constituent RF operating bands for further processing. Those skilled in the art will appreciate that the one of the primary antenna 12 and the secondary antenna 14 coupled to the front end diplexer 20 is dependent on current signal conditions, and that the primary antenna 12 and the secondary antenna 14 may be dynamically swapped as desired in order to improve transmission and/or reception characteristics.
The front end diplexer 20 is configured to separate RF receive signals from one of the primary antenna 12 and the secondary antenna 14 into low-band RF receive signals and mid/high-band RF receive signals, separately delivering the low-band RF receive signals to a low-band RF signal node 30 and the mid/high-band RF receive signals to the reconfigurable RF filtering circuitry 22. Further, the front end diplexer 20 is configured to combine RF transmit signals from the low-band RF signal node 30 and the reconfigurable RF filtering circuitry 22 and provide these RF transmit signals to one of the primary antenna 12 and the secondary antenna 14 for transmission.
As discussed above, it is generally difficult for a filter to achieve the necessary bandwidth for passing mid-band RF signals and high-band signals while maintaining adequate selectivity to separate RF signals at the edges of these frequency bands. Accordingly, the reconfigurable RF filtering circuitry 22 includes a first reconfigurable RF filtering circuitry diplexer 32A, a second reconfigurable RF filtering circuitry diplexer 32B, and a number of reconfigurable RF filtering circuitry switches SWRFC. The first reconfigurable RF filtering circuitry diplexer 32A is configured to separate RF signals within the mid-band from RF signals within a first subset of the high-band, while the second reconfigurable RF filtering circuitry diplexer 32B is configured to separate RF signals within the mid-band from RF signals within a second subset of the high-band. The first subset of the high-band may include a relatively narrow portion thereof at the lower end of the band (e.g., from 2300 MHz to 2400 MHz), while the second subset of the high-band may include the remaining portion of the high-band (e.g., 2400 MHz to 2700 MHz). Due to the relatively narrow portion of the high-band passed by the first reconfigurable RF filtering circuitry diplexer 32A, the selectivity of this portion of the diplexer may be significantly improved such that the first reconfigurable RF filtering circuitry diplexer 32A can adequately separate mid-band RF signals (even those at the upper end of the mid-band) from high-band RF signals at the lower end thereof.
In carrier aggregation configurations in which mid-band RF signals are simultaneously received along with high-band RF signals and the mid-band RF signals are relatively close in frequency to the high-band RF signals, the reconfigurable RF filtering circuitry switches SWRFC are configured to couple the first reconfigurable RF filtering circuitry diplexer 32A between the first band filtering circuitry 24, the second band filtering circuitry 26, and the front end diplexer 20. Accordingly, RF receive signals within the mid-band and the high-band that are relatively close in frequency can be adequately separated by the first reconfigurable RF filtering circuitry diplexer 32A and delivered to the first band filtering circuitry 24 and the second band filtering circuitry 26. In carrier aggregation configurations in which mid-band RF signals are simultaneously received along with high-band RF signals and the mid-band RF signals are relatively far apart in frequency to the high-band RF signals, the reconfigurable RF filtering circuitry switches SWRFC are configured to couple the second reconfigurable RF filtering circuitry diplexer 32B between the first band filtering circuitry 24, the second band filtering circuitry 26, and the front end diplexer 20. Accordingly, RF receive signals within the mid-band and the high-band that are relatively far apart in frequency can be adequately separated by the second reconfigurable RF filtering circuitry diplexer 32B and delivered to the first band filtering circuitry 24 and the second band filtering circuitry 26. In non-carrier aggregation configurations, the reconfigurable RF filtering switches SWRFC are configured to directly couple one of the first band filtering circuitry 24 and the second band filtering circuitry 26 to the front end diplexer 20. The first reconfigurable RF filtering circuitry diplexer 32A and the second reconfigurable RF filtering circuitry diplexer 32B can by bypassed in this case since the RF receive signals will fall within a single one of the mid-band and the high-band. Accordingly, in non-carrier aggregation configurations in which the first reconfigurable RF filtering circuitry diplexer 32A and the second reconfigurable RF filtering circuitry diplexer 32B are not necessary, the insertion loss associated therewith can be avoided.
The first band filtering circuitry 24 and the second band filtering circuitry 26 include a number of band filtering switches SWBF and a number of band filters 34. The band filtering switches SWBF are configured to couple one or more of the band filters 34 to the reconfigurable RF filtering circuitry 22. Each one of the band filters 34 is configured to isolate an RF signal within a particular RF operating band (or in some cases, RF signals within multiple RF operating bands) from other RF signals. RF receive signals from the reconfigurable RF filtering circuitry 22 are isolated via an appropriate band filter 34 and delivered to an appropriate one of a number of input/output nodes 36. RF transmit signals from downstream circuitry are received at one of the input/output nodes 36, isolated from other RF signals via an appropriate band filter 34, and delivered to the reconfigurable RF filtering circuitry 22 for transmission from one of the primary antenna 12 and the secondary antenna 14. Generally, only the band filters 34 associated with the particular RF operating bands being transmitted or received are coupled to the reconfigurable RF filtering circuitry 22 to avoid excessive loading of the signal paths.
Control circuitry 38 is coupled to each one of the primary antenna swapping circuitry 16, the secondary antenna swapping circuitry 18, the reconfigurable RF filtering circuitry 22, the first band filtering circuitry 24, and the second band filtering circuitry 26 in order to control the state of the switches therein and effectuate the functionality discussed below.
Due to the reconfigurable RF filtering circuitry 22, the RF front end circuitry 10 is capable of separating any combination of mid-band RF signals and high-band RF signals, thereby expanding the range of band combinations for carrier aggregation and/or MIMO. However, the configuration of the switches in the primary antenna swapping circuitry 16, the secondary antenna swapping circuitry 18, the reconfigurable RF filtering circuitry 22, the first band filtering circuitry 24, and the second band filtering circuitry 26 may introduce excessive insertion loss in the signal paths thereof. FIG. 2A shows a switch configuration in which the first reconfigurable RF filtering circuitry diplexer 32A in the reconfigurable RF filtering circuitry 22 is used to perform carrier aggregation between one or more mid-band RF signals and one or more high-band RF signals via the primary antenna 12. As shown, a second one of the primary antenna swapping switches SWPAS2 is closed, while the remaining primary antenna swapping switches SWPAS are open. Further, a second one of the reconfigurable RF filtering circuitry switches SWRFC2, a sixth one of the reconfigurable RF filtering circuitry switches SWRFC6, and a seventh one of the reconfigurable RF filtering circuitry switches SWRFC7, are closed, while the remaining reconfigurable RF filtering circuitry switches SWRFC are open. For exemplary purposes, a fourth one of the band filtering switches SWBF4 is closed in the first band filtering circuitry 24 while the remaining band filtering switches SWBF are open. Similarly, a first one of the band filtering switches SWBF1 is closed in the second band filtering circuitry 26 while the remaining band filtering switches SWBF are open.
Assuming a 0.20 dB insertion loss for each closed series switch in the signal path and a 0.025 dB insertion loss for each open parallel switch, a signal path from the primary antenna 12 to a second one of the input/output nodes 36B includes four closed series switches and ten open parallel switches for a total insertion loss of 1.05 dB. Notably, this is a conservative estimate of the actual insertion loss, as a number of band filtering switches SWBF associated with additional band filters 34 in the first band filtering circuitry 24 and the second band filtering circuitry 26 are not shown to avoid obscuring the drawings. A similar result is achieved when the second reconfigurable RF filtering circuitry diplexer 32B in the reconfigurable RF filtering circuitry 22 is used to perform carrier aggregation between one or more mid-band RF signals and one or more high-band RF signals via the primary antenna. Additional switches are added in the signal path when the secondary antenna 14 is used in these configurations.
FIG. 2B shows a switch configuration in which the first reconfigurable RF filtering circuitry diplexer 32A and the second reconfigurable RF filtering circuitry diplexer 32B are bypassed in a non-carrier aggregation mode. In the particular example shown in FIG. 2B, the primary antenna 12 is coupled via the front end diplexer 20 to the first band filtering circuitry 24. Accordingly, a second one of the primary antenna swapping switches SWPAS2 is closed, while the remaining primary antenna swapping switches SWPAS are open. Further, a first one of the reconfigurable RF filtering circuitry switches SWRFC1 is closed while the remaining reconfigurable RF filtering circuitry switches SWRFC are open. For purposes of example, a fourth one of the band filtering switches SWBF4 in the first band filtering circuitry 24 is closed while the remaining band filtering switches SWBF are open.
Again assuming a 0.20 dB insertion loss for each closed series switch in the signal path and a 0.025 dB insertion loss for each open parallel switch, a signal path from the primary antenna 12 to the second one of the input/output nodes 36B includes three closed series switches and ten open parallel switches for a total insertion loss of 0.825 dB. Once again, this is a conservative estimate of the actual insertion loss, as a number of band filtering switches SWBF associated with additional band filters 34 in the first band filtering circuitry 24 and the second band filtering circuitry 26 are not shown to avoid obscuring the drawings. A similar result is achieved when only the second band filtering circuitry 26 is coupled to the front end diplexer 20.
The insertion loss added by the switching elements in the RF front end circuitry 10 may degrade the performance thereof, causing excessive power loss and thus reducing battery life of mobile wireless devices. Accordingly, there is a need for improved RF front end circuitry capable of supporting carrier aggregation and/or MIMO configurations between RF signals that are relatively close in frequency to one another.